This year marks the fourth year of the International Working Conference on Active Networks; this volume contains the papers accepted for full presentation at the conference. These proceedings are proof that Active Networks is a vibrant ?eldwithtrulyinternationalparticipation,withresearchdonenotonlyinthe contextofformalprograms(suchasFAINandDARPAActiveNets),butalso in a number of independent research programs. We received signi?cantly more submissions than could possibly be accom- datedduringthetwodaysofsessions,andcombinedwiththedesireforhigh standards this has resulted in a very selective program. The distinguished p- gramcommitteedidanoutstandingjobofreviewingthepapers,withdetailed commentsandsuggestionstotheauthors,eachpaperreceivingfrom4to6 reviews.Ofthe53paperssubmitted,9wereacceptedunconditionally.Anad- tionalsetofpaperswereconditionallyaccepted,withprogramcommitteem- bers working with the authors to insure that review concerns were addressed, while shepherding towards ?nal publication; 11 of these papers are included in the proceedings.An additional set of poster presentations were given for worthy submissionsthatcouldnotbeaccommodatedwithintheselimitations,aswell as position papers and work in progress. ThebestpaperawardwenttoNadiaShalaby,YitzchakGottlieb,andMike Wawrzoniak for "Snow on Silk: A NodeOS in the Linux Kernel," which begins these proceedings and the papers in the node operating systems session. These proceedingsalsocontainactivenetworkingpaperson:servicedeployment,d- covery,andcomposition;monitoringandmanagement;mobilewireless;system architecture; and peer-to-peer and group communication. In keeping with the "working"natureoftheconference,signi?canttimewasreservedfordiscussion, andpanelsonactivemobilenetworking,peer-to-peer,andthefutureprospects for active network research and deployment. We would like to thank the technical program committee members for their hard work in reviewing and shepherding papers. We would like to thank Be- hardPlattner,PlaciFlury,andLukasRuffortheirconsiderabletimeandsupport inconferenceorganization,andforprovidingtheinfrastructureattheSwissF- eralInstituteofTechnology(ETH),Zurich that made the work of the program committee considerably easier.And of course it is the work of the authors that isthecoreoftheseproceedings,andtheattendees'participationthatmakesfor an outstanding working conference. We hope you enjoy the fruits of their labor.
